Add TODOs for performance aspects

Signed-off-by: Olivier <olivier@librepush.net>

yama/src/scan.rs

@@ -129,6 +129,8 @@ pub fn scan(root: &Path, ignores: &Vec<String>) -> eyre::Result<PatriciaMap<Scan
             .build()
             .context("failed to create overrides with ignore entries")?,
     );
+
+    // TODO(performance): We could use `WalkParallel` if we restructure this code.
     let walker = walker.build();
 
     for entry in walker {
@@ -195,6 +197,7 @@ fn scan_one_no_recurse(path: &Path, metadata: Metadata) -> eyre::Result<Option<S
             size: metadata.size(),
         }))
     } else if filetype.is_dir() {
+        // TODO(perforance): this call is very likely wasteful
         let dir_read = path.read_dir();
 
         if let Err(e) = &dir_read {